San Francisco Mayor Willie Brown yesterday extended his vision of a revitalized public transit system, visualizing buses equipped with earsplitting alarms and shuttle vans that would pick up passengers at their front doors.

For the second day in a row, Brown zeroed in on the much-maligned Municipal Railway, this time telling a meeting of the Senior Action Network that the system is wasting time and money by routinely running nearly empty buses.

"We could pick up that rider, deliver the rider to where the rider needs to go at a cost far less than rolling empty coaches back and forth," said Brown.

The mayor said he has repeatedly seen buses on the 38 Geary line -- which runs from downtown to the ocean -- roll virtually vacant for miles. During the predawn hours, in particular, only the bus driver is riding the stretch from 48th Avenue to 20th Avenue, he said.

The solution, Brown said, is to shut down the largely unused portion of the route in favor of "a super shuttle" to at least take the rider to a more heavily used place along the line.

"It would be cool if I could pick up the telephone and call the appropriate number, and within 10 to 12 minutes there was a super shuttle thing that said 'Muni' on the side at my door," said Brown. "We would save a tremendous amount of money and it would be far more efficient . . . and far safer."

Brown said he has studied the idea and is convinced that it would be a more cost-effective way to run the system, but he had no figures or data yesterday to bolster his claim.

The mayor, who made safety on Muni the centerpiece of his election campaign, also proposed junking the buses' silent alarms and refitting the fleet with ear- splitting systems that would summon help when needed.

"Get the alarm that makes the maximum amount of noise and attracts the maximum amount of attention," said Brown. "I suspect that anybody doing anything bad on the bus would be so shocked by the noise -- and everybody's eyes focused on the bus -- that almost instantly they would cease doing what they are doing."

The proposal comes a day after Brown suggested eliminating fares on buses altogether, primarily to protect drivers from a growing number of passengers who refuse to pay.

Brown admitted that he had not completely flushed out the fare-free plan yet, but he said he was encouraged by the city's Chamber of Commerce, which has embraced the notion of a separate financing source for mass transit.

"I haven't seen what they want to do, but I am delighted that they have finally come to the reality that we need a dedicated source of revenue" for Muni, Brown said. "If we can figure out some way for all of us in the city to make a contribution to (Muni) and thereby get the right to ride Muni at any time, we would increase ridership . . . and have no robberies as a result of the Muni fare box."

"We had kids skipping school because the no-fare system allowed them to ride wherever they wanted to go," said spokeswoman Polly Munguia. "Homeless people would ride all day long, especially in inclement weather. We had hygiene problems . . . We even had problems with people stealing something, then hopping on the bus to get away."

Brown, nonetheless, is unfazed. "Someone said, 'This is just another one of Willie Brown's harebrained ideas.' But at least I have ideas. I'm full of ideas," he said.